A male cell (arrow), presumably fetal in origin, in the liver tissue from a woman with autoimmune hepatitis

A new study indicates that male DNA, left over from pregnancy with a male fetus, can persist in a woman’s brain throughout the rest of her life. Although the exact biological impact of the DNA is yet unclear, the study found that women with more male DNA in their brains were less likely to suffer from Alzheimer’s disease, suggesting that male DNA could help protect mothers from this disease.